PROJECT SUMMARY/ABSTRACT The US population is rapidly aging. It is projected that by 2030, more than 20% of the population will be over 65 years of age1. Aging is accompanied by increased metabolic and cardiovascular disease. An important tissue to combat metabolic disease and influence heart function is brown adipose tissue (BAT). Brown adipose tissue (BAT) is a thermogenic tissue that has a high capacity for both glucose and lipid oxidation, making BAT a potential target to decrease plasma glucose and lipids and to protect against obesity and it's co- morbidities, including type 2 diabetes and cardiovascular disease (CVD). Increasing the amount of BAT by transplantation improves metabolic health, reduces adiposity, and increases glucose uptake into the heart. BAT has great potential as a therapeutic target to combat both metabolic and cardiovascular disease, but BAT decreases with age. Thus, we hypothesized that increasing BAT could be a potential therapeutic to improve the metabolic and cardiovascular impairments that occur with aging. Our preliminary data demonstrate that transplantation of BAT into an aged mouse (18 months) improves metabolic and cardiovascular health. We have also generated exciting data showing that exercise increases the signaling lipid 12,13-diHOME from BAT in humans. 12,13-diHOME is decreased with age in both humans and mice, while exercise in an elderly population restores 12,13-diHOME to concentrations similar to young adult subjects. Injection of this lipid into mice has a direct effect on the heart, increasing left ventricular pressure development. Taken together, our exciting preliminary data show that 1) transplantation of BAT improves metabolic and cardiovascular health in an aged mouse; 2) exercise-training increases the signaling lipid 12,13-diHOME; 3) concentrations of 12,13- diHOME are decreased with age in humans and mice; and 4) injection of 12,13-diHOME in mice directly affects heart function. Here, we will test the novel paradigm that BAT exerts endocrine effects that improves metabolic health and cardiac function in senescence with three specific aims: 1) Determine the role of BAT on age-induced impairments in metabolism and insulin sensitivity; 2) Determine the role of BAT on the age- induced impairments in cardiac function; and 3) Determine if BAT mass and endocrine function is linked with metabolism or cardiac function in older adults. This project will establish if increasing BAT, and specifically the lipid 12,13-diHOME, negates the metabolic and cardiovascular impairments that occur with senescence in rodents and humans. The proposed studies have the potential to elucidate a novel role, and potential therapeutic approach, for BAT to negate the detrimental effects of aging. .